A helicopter or the like is fitted with a rotor that is driven in rotation by engine means, in particular by turbines. The rotor is also fitted with a main brake mechanism to prevent the rotor from turning after the engine means have stopped. The main brake mechanism is conventionally a mechanism of the type comprising a,disk that is clamped between jaws carrying brake linings, and is of the type that is under manual control that provides sufficient force to prevent the rotor from turning against its own inertia when it is no longer driven by the engine. It should be observed that in order to avoid excessive heating of the brake linings and corresponding premature wear thereof, the main brake mechanism is fitted with detector means to prevent the engine means from being operated while the rotor is being braked. In practice, the pilot usually waits for a freely rotating rotor to reach a speed of rotation that is below a threshold that is tolerable for operating the brake mechanism.
There is also a problem of the rotor rotating under a strong wind, during both take-off and landing of the helicopter. In particular, in order to start up a rotor under such weather conditions, it is helpful to prevent the rotor from moving during the initial stages of putting the engine means into operation.
It can be seen that the braking force to be generated is large and that the above-mentioned manually-controlled brake mechanisms are insufficient and inappropriate. This problem is made particularly difficult to solve for heavy helicopters where the power of the engine means is proportionate to the mass of the vehicle. It has been proposed to fit such helicopters with a brake mechanism in which the jaws are driven hydraulically, and are thus capable of generating suitable, large braking forces. Such mechanisms are commonly organized in such a manner as to apply selective braking forces depending on weather conditions and on the starting and/or stopping stages of the rotor. It should be observed, as mentioned above, that the braking forces applied are selected in association with authorization to operate or not operate the various engine means for driving the rotor during an initial starting stage.
Nevertheless, it can be seen that the use of such brake devices that are driven and controlled hydraulically leads to a structure that is complex and heavy. In addition, the heating generated by braking the rotor and the location of hydraulic members close to the rotor transmission box requires safety means to be provided against the risk of fire.
In order to avoid ubiquitous use of hydraulic members, proposals have also been made for a hybrid brake mechanism for a helicopter rotor of the type comprising a disk mechanism under manual control, in which the jaws are driven to clamp the disk under the control of a lever for setting the hydraulic means into operation. The hydraulic means generate a force that is appropriate for secondary braking under strong winds, and they also satisfy the requirements for the necessarily-lower forces that are sufficient for main braking. For example, reference can be made to document FR 2 683 503 (Aerospatiale).
Nevertheless, it should be observed that in this field, when it comes to organizing rotor brake means, there is a constraint that not only must the means be as simple and as lightweight as possible, but they must also take up as little space as possible.
As a result, in general, designers tend to look for solutions that provide a compromise between all of the above-mentioned constraints, in order to organize the rotor brake means, both main brake means for use after the rotor drive engine means have stopped, and secondary brake means for use under strong winds, in particular so that they comply with satisfactory conditions in terms of safety, for bulk, complexity, and weight that must be kept as small as possible and/or must be as well adapted as possible to the type of helicopter involved, in particular in relation to the weight of the helicopter.